Hydrocarbon solvent refining process



Feb. 28, 1967 l P. P. BOZEMAN, JR.. ET AL 3,305,849

HYDROCARBON SOLVENT REFINING PROCESS Filed Aug. 2v. 1964 2 shams-snee*b1 Feb. 28, 1967 P. P. BOZEMAN, JR., ET AL HYDROARBON SOLVENT REFININGPROCESS Filed Aug. 27. 1964 2 Sheets-Sheet 2 .Wma

United States Patent O ,306,849 HYDROCARBON SOLVENT REFINING PROCESSPaul P. Bozeman, Jr., Groves, and Robert A. Woodle, Nederland, Tex.,assignors to Texaco Inc., New York, NX., a corporation of Delaware FiledAug. 27, 1964, Ser. No. 392,416 6 Claims. (Cl. 208-314) This inventionrelates to a hydrocarbon treating process employing liquid-liquidsolvent extraction. More particularly, it relates to an improved methodof recovering the solvent in the solvent refining of a petroleumfraction, for example, a gas oil or a lubricating oil stock.

In accordance with the process of this invention, a hydrocarbon oil iscontacted with a solvent in a first solvent extraction zone formingraffinate and extract-mix phases. The extract-mix phase is cooledeffecting separation of a hydrocarbon phase from a remaining extractmixphase of reduced hydrocarbon content. The remaining extract-mix phase iscontacted with a low boiling hydrocarbon solvent in a second extractionzone effecting re-extraction of the hydrocarbons from the selectivesolvent. Raffinate from the second extraction zone comprising selectivesolvent is returned to the primary extraction zone and the newextract-mix phase comprising hydrocar-bon oil extract and low boilinghydrocarbon solvent is subjected to distillation separating said ilowboiling hydrocarbon solvent which is returned to the second extractionstep. Extract oil is withdrawn as distillation bottoms.

Solvent extraction is widely used in the petroleum industry to effectfractionation of hydrocarbon oil. Substances of low hydrogen to carbonratio, for example, aromatic hydrocarbon and polar substances such assulfur compounds are relatively soluble in solvents such as furfural,other aldehydes such as benzaldehyde, phenol, nitrobenzenes, ketones,etc. Although other solvents may be employed in the process of thisinvention, we prefer to employ furfural which is low in cost, readilyavailable, and possesses superior solvent characteristics. When ahydrocarbon oil containing mixtures of hydrocarbons of high and lowhydrogen to carbon ratio and polar substances is contacted with such asolvent, the hydrocarbons of low hydrogen to car-bon ratio and polarsubstances are extracted from a raffinate comprising the more parafiinichydrocarbons of high hydrogen to carbon ratio. The raffinate phasecomprises oil with a relatively small amount of dissolved solvent andthe extract-mix phase contains the bulk of the solvent and a relativelysmall amount of dissolved oil and polar compounds. The extract-mix andrafiinate phases are then fractionated to separate solvent for recycleto the extraction ysystem from the refined oil product and extract.Since the raffinate phase comprises oil with a relatively small amountof dissolved solvent, this solvent may be advantageously separated bydistillation with steam or by washing with water. In the case offurfural, the furfural is separated as a steam-furfural azeotrope Iwhichhas a boiling point of 208 F. at 760 mm. When furfural is recovered bywashing the rafiinate with water, the furfural is recovered from thewater washings by distillation, again as the azeotrope boiling at 208 F.

The extract-mix phase contains the bulk of the solvent with only arelatively small amount of dissolved hydrocarbon. Heretofore, thesolvent has usually been separated by distillation wherein most of thesolvent is separated by distillation in the absence of steam at itsboiling point which when the solvent is furfural, is 323 F. at 760 mm.Separation in the absence of steam is desirable since otherwise aninordinately large amount of azeotrope is produced which must beredistiilled for separation of dry solvent. In steam stripping, there isa tendency to 3,306,849 Patented Feb. 28, 1967 Mice entrain low boilingconstituents of the hydrocarbon feed in the relatively large amount ofsolvent-water azeotrope distilled overhead which results in oil dilutionof the solvent. When distilling furfural from extract-mix from theextraction yof high boiling oils, for example, vacuum residue, the highdistillation temperatures encountered foster polymerization anddecomposition of the furfural. Although the amount of polymerization anddecomposition occurring may be small, the products of polymerization anddecomposition are solid coke-like materials. These polymerization anddecomposition products tend to foul heat exchange surfaces therebyreducing the efiiciency of heat transfer and reducing the throughputwhich may be obtained in the furfural recovery equipment.

It is an objective of the process of this invention to provide a meansof separating solvent from the extractmix of a solvent refining processwithout high temperature distillation. Another objective is to producean extract fraction of intermediate quality. Another advantage of theprocess of this invention is that in solvent refining with furfural,furfural distillation is eliminated in favor of light oil distillationwith savings in heat due to dstillation of less material with lower heatof vaporization. A further objective is that furfural polymerization anddecomposition and attendant fouling of towers and exchangers arereduced.

In accordance with this invention, extract-mix from the solventextraction of a hydrocarbon oil at a temperature within the range ofabout 140 to 240 F. is cooled to approximately 100 F. effectingseparation of about 30 to 50 percent of the extract 'oil contained inthe extractmix as an intermediate oil phase. This intermediate oil.phase is separated and remaining extract-mix comprising to 96 volumepercent solvent and 4 to 10 percent extract oil is contacted with alight hydrocarbon solvent. Suitable light hydrocarbon solvents includeliquidified petroleum gases including propane which has a boiling pointof 44 F. and other liquid petroleum fractions boiling up to about 500 F.The light hydrocarbon solvent is desirably parafiinic in nature, thatis, comprised principally of aliphatic hydrocarbons. The endpoint of thehydrocarbon solvent should be at least below the initial boiling pointof the charge oil to the furfural treating process to facilitateseparation of the light hydrocarbon solvent from the extract product bydistillation. The light hydrocarbon solvent is applied to theextract-mix at a solvent dosage of about l to 2 volumes -of lighthydrocarbon per volume of extract-mix. An extraction temperature ofabout 100 F. is employed. Under these conditions the hydrocarbon contentof the extract-mix is transferred from the extract-mix to the lighthydrocarbon solvent forming a raffinate comprising furfural essentiallyfree of extract oil. Desirably, the furfural raffinate is heated andpassed to a stripping zone wherein any dissolved water or lighthydrocarbon is removed and the stripped furfural is recycled for reusein the primary solvent extraction. The light hydrocarbonextract oilmixture leaving the solvent regeneration extractor is distilled torecover the extract oil and separate the light hydrocarbon solvent forreuse.

In accordance with this invention, the solvent an extract oil areseparated from the extract-mix in two stages, the first stage ofseparation being effected by cooling and the second stage being effectedby re-extraction of remaining extract-mix with a light parafiinicsolvent. In the first step, the extract-mix is cooled from the primarysolvent extraction outlet temperature within the range of about to 240F. to a temperature Within the range of about 90 to 120 F. andpreferably about 100 F. In this cooling step, approximately 30 to 50percent of the oil contained in the extract-mix separates as ahydrocarbon phase. This hydrocarbon phase is separated and may beutilized as an intermediate oil. In addition, the cooling stepcooperates with the succeeding re-extraction step -by enabling the lighthydrocarbon solvent to displace a `greater amount of extract hydrocarbonfrom the extract-mix or to effect a given extraction with a lesseramount of light parainic solvent than would be required at thetemperature of the primary extract-mix outlet. Cooling may be effectedby indirect heat exchange with cold water or by adding cold lightparafiin hydrocarbon solvent. Cooling water may be provided byconventional cooling towers or may be chilled by refrigeration torautorefrigeration. Cooling by the addition of light paraffin hydrocarbonis advantageous in dealing with extract containing wax or othermaterials of high pour point.

The accompanying drawings diagramm-atically illustrate the process ofthis invention. Although the drawings illustrate :arrangements ofapparatus in which the process of this invention may be practiced, it isnot intended to limit the invention to the particular materials orapparatus described.

FIGURE l illustrates the process of this invention with the separationof an intermediate oil.

FIGURE 2 illustrates an embodiment of the process of this inventionwherein a plant designed for separation of furfural from the extract-mixby distillation is modified to employ the cooling and re-extractionprocess of this invention.

Referring to FIGURE l, oil feed, for example, a lubricating oil stock,in line 1 is passed to treating tower 2 wherein the oil feed iscountercurrently contacted with solvent introduced through line 3forming extract-mix and raffinate phases. Raffinate phase is withdrawnthrough line 4 and passed to refined oil stripping tower 5. In refinedoil stripping tower 5, solvent is separated by distillation through line6 for recovery and reuse and refined oil free of solvent is dischargedthrough line 7 for blending or further refining.

Extract-mix from tower 2 is withdrawn through line 10, cooled in cooler11 and passed through line 12 to phase separator 13. Cooling of theextract-mix causes a hydrocarbon phase to separate from the extract-mix.This hydrocarbon phase is withdrawn from the top of phase separator 13through line 15 and is passed to intermediate oil stripping tower 16. Intower 16 the hydrocarbon phase is stripped separating the dissolvedsolvent through line 17 for reuse in the extraction process. Thestripped intermediate oil is withdrawn through line 18 for furtherrefining or blending.

Extract-mix phase from separator 13 is withdrawn through line 20 andpassed to solvent recovery tower 21. In solvent recovery tower 21, theextract-mix phase is countercurrently contacted with light paraftinichydrocarbon introduced into tower 21 through line 22. Solventsubstantially free of extract oil is withdrawn from the bottom ofsolvent recovery tower 21 through line 3 for return to treating tower 2.Light hydrocarbon and dissolved extract voil are withdrawn from the topof solvent recovery tower 21 through line 25 and passed to extractstripping tower 26. In extract stripping tower 26, the light hydrocarbonis separated las distillate and returned to solvent recovery tower 21through line 22. Stripped extract is discharged through line 27 forfurther refining or use.

With reference to FIGURE 2, oil feed in line 35 is passed to treatingtower 36 and countercurrently contacted with furfural solvent introducedinto tower 36 through line 37. Rafiinate comprising refined oil :andcontaining a small amount of dissolved furfural is withdrawn throughline 39 and passed to solvent recovery facilities not shown. Theextract-mix, at an outlet temperature within the range of about 140 to240 F., is

withdrawn from tower 36 through line 40. Extract-mix in line 40 ispassed through cooler 45 where the temperature Iis reduced to about 90to 120 F. Cooled extractmix is passed through line 46 to phase separator47. In phase separator 47, the lighter hydrocarbon phase separates andis withdrawn through line 50u The remaining extract-mix containing areduced yamount of dissolved hydrocarbon is withdrawn through `line 51to solvent regeneration tower 52 wherein it is countercurrentlycontacted with light hydrocarbon introduced through line S3. In tower52, the extract hydrocarbon is re-extracted from the furfural and thelatter is withdrawn as rafiinate through line 54. Light hydrocarbons andre-extracted hydrocarbons are withdrawn through line 55, and passedthrough heat exchanger 56, line 57, heat exchanger 58 and line 59 toatmospheric flash tower 60.

In flash tower 60, the light hydrocarbon is separated as distillate atabout atmospheric pressure and is withdrawn through line 65. The lighthydrocarbon distillate is condensed in exchanger 56 and passed throughline 66 to line 53 for reuse in solvent regeneration tower 52. Bottomsfrom flash tower 60 -comprising extract hydrocarbons and some lighthydrocarbon are withdrawn through line 67 and heated in heater 68. Theresulting heated light hydrocarbon-extract mixture is passed throughline 69 to pressure flash tower 70 maintained at a pressure of about 30p.s.i.g. In pressure fiash tower 70, the remaining light hydrocarbon isflashed and withdrawn as distillate through line 71. The distillate iscooled in heat exchanger 58 and passed through line 72 and combined withthe light hydrocarbon distillate in line 53. The flashed extracthydrocarbon from the bottom of tower 70 is withdrawn through line 75,combined with the hydrocarbon phase in line 50, and the mixture ispassed to vacuum steam stripper 76.

In steam stripper 76 a small amount of dissolved furfural is removedfrom the extract oil by stripping with steam introduced through line 77.Vapors of furfural and steam are withdrawn through line 78. Thefurfural-water vapor mixture in line 78 is passed through line 79,cooler 80 and line 81 to separating drum 82. Separating drum 82 isprovided with weirs 83 and 84. Furfural layer containing a small amountof dissolved water and dissolved hydrocarbon -separates in the endcompartment of separator 82 behind Weir 83. Furfural layer is withdrawnthrough line and combined with the furfural in line 54. The water phaseand light hydrocarbon phase overfiow weir 83 and separate into a heavierwater phase which accumulates between weirs 83 and 84 and lighthydrocarbon which overfiows Weir 84 and is collected in the other endcompartment. Water phase is withdrawn through line 86 and passed towater stripper 87. In water stripper 87 an azeotrope of furfural andwater is separated as distillate through line 88 and water free offurfural is withdrawn through line 89. The vapors in line 88 arecondensed in cooler 90 and passed through line 91 to line 81 and tophase separator 82. Light hydrocarbon layer is withdrawn from separator82 through line 95 and is combined with the hydrocarbon in line 53 foruse in solvent recovery tower 52.

The furfural phase in line 85 and line 54 are passed to furfural dryingtower 96. In tower 96, an azeotrope of furfural and water is removed asdistillate through line 97 and combined with the furfural-water vaporsin line 79 for condensation and eventual return to separator 82. Driedfurfural is withdrawn from the bottom of fnrfural tower 96 through line37 for return to treating tower 36.

Example l A lubricating oil stock is furfural refined producing arefined oil of SAE l0 grade. The lubricating oil stock has the followingcharacteristics: gravity, API 28.8; flash, COC, F. 410; viscosity,SUS/100 F. 158; viscosity, SUS/210 F. 43.0; VI 82.0; pour, F. 75; color,Lovibond 1/2 cell 45; refractive index at 70 C., 1.4730.

The lubricating oil stock at a rate of 5,000 barrels per day iscontacted with furfural at a dosage of 350 percent, in a rotating discconta-ctor. Rafnate i-s withdrawn at 230 F. and is stripped producing3,500 barrels per day of refined oil of the following quality; gravity,API 33.5; flash, COC, F. 410; viscosity, SUS/100 F. 122; viscosity,SUS/210 F. 41.6; VI 112; pour, F. 90; color, Lovibond 6" cell 50;refractive index 1.4540. Extractmix containing 8.2 volume percentextract oil is withdrawn at 185 F. at a rate of 18,382 barrels per day.The extract-mix is cooled to 100 F. separating 469 barrels per day ofintermediate oil phase containing 4 percent dissolved furfural. Theintermediate oil phase is stripped separating 450 barrels per day ofintermediate oil having a gravity of 28.0 API, a COC flash of 400 F.; aviscosity -of 45.0 SUS/210 F.; a VI of 78.0; and a refractive index of1.4740. Extract-mix phase at 100 F. and containing 5.9 volume percentextract oil is re-extracted at 100 F. by contacting with 22,390 barrelsper day of a light paraffinic solvent in a second rotating disccontactor. The light parat-linie solvent comprises 97 volume percentparaffinic hydrocarbons and boils within the range of 211 to 348 F. byASTM distillation. Ra'inate comprising furfural containing 8.2 volumepercent hydrocarbon is stripped separating a small amount of dissolvedlight hydrocarbon and water and is recycled to the primary lubricatingoil contacting step. Extract-mix from the re-extraction step comprising90 volume percent light parainic solvent and 4.5 vol-ume percent extractoil is separated and redistilled producing 1050 barrels per day ofextract oil and 21,000 barrels per day of light parafiinic solvent. Theextract oil has a gravity of 15.2 API; a COC fiash of 400 F. and arefractive index of 1.5362.

Example Il A feature of this invention is that the secondary orreextraction step is effected at a lower temperature than the primaryextraction. This lower temperature of reextraction results in greatlyincreased re-extraction efficiency. The effect of temperature on theamount of oil displaced by re-extraction of an extract-mix from thesolvent extraction of a cracked light cycle gas oil with a lightparaffinic solvent is shown in Table I:

The effect of temperature on the amount of oil displaced from anextract-mix containing 33 volume percent extract oil is shown in TableII:

TABLE 1I Furfural Light Parafin Extract-Mix Extract Oil Dosage, Vol.Rex-extraction Light Parafrn Yield, Wt.

Percent Dosage, Vol. Contacting Percent Percent Temp., F.

Table II shows a 30.8 percent yield reduction upon reextraction at 134F. whereas at 100 F. a corresponding yield reduction of 35.0 percent isobtained. Tables I and II show that at lower temperatures, the lightparaffin solvent displaces more oil from the extract-mix than at highertemperatures.

We claim:

1. A method of treating a hydrocarbon oil wherein said oil is contactedwith a selective solvent comprising furfural in a first solventextraction zone under conditions forming a first rainate phase and afirst extract-mix phase, which comprises withdrawing said firstextract-mix phase at -a temperature within the range of about 140 to 240F.,

cooling said rst extract-mix phase to a temperature within the range ofabout 90 to 120 F., separating a second raffinate comprising hydrocarbonoil extract and dissolved solvent and a second extract-mix phasecomprising solvent and remaining hydrocarbon extract oil,

contacting said second extract-mix phase with a liquid paraffinhydrocarbon fraction boiling within the range of about -44 to 500 F. andhaving an end point of least F. below the initial boiling point of saidhydrocarbon oil in a second extraction Zone forming a third rafiinatephase comprising said selective solvent and a third extract-mix phasecomprising said remaining hydrocarbon oil and said low boilinghydrocarbon,

recycling at least a part of said third raffinate phase to said rstsolvent extraction zone as at least a portion of said selective solvent,

separating hydrocarbon extract oil from said secondary raffinate, and

separatin-g remaining hydrocarbon oil extract from said thirdextract-mix.

2. The process of claim 1 wherein said second extractmix is passed tosaid second extraction zone at the temperature at which it is formed.

3. In a hydrocarbon oil treating process wherein a hydrocarbon oil feedis contacted with a solvent feed comprising fnrfural in a primaryextraction zone separating a raffinate comprising refined oil anddissolved solvent and a first extract-mix comprising solvent anddissolved extract oil, the improvement which comprises withdrawing saidrst extract-mix at a temperature within the range of about 140 to 240F.:

cooling said first extract-mix phase to a temperature within the rangeof about 90 to 120 F. effecting separation of a hydrocarbon phasecomprising within the range of about 30 to 50 percent of the extract oilcontained in said extract-mix and dissolved solvent and a remainingextract-mix phase comprising solvent and dissolved remaining extractoil,

stripping dissolved solvent from said hydrocarbon phase separating afirst extract product and solvent for recycle to said primary extractionzone as a portion of said solvent feed, c-ontacting said remainingextract-mix phase with a paraliinic hydrocarbon liquid boiling withinthe range of -44 to 500 F. and who-lly at least 100 F. bel-ow theboiling range of said hydrocarbon oil feed in a secondary extractionzone effecting formation of a second raffinate phase comprising solventsubstantially free of said remaining extract oil an-d a secondextract-mix phase comprising said paraiinic hydrocarbon liquid anddissolved remaining extract oil,

recycling at least a part of said second raffinate phase to said primaryextraction zone as a portion of said solvent feed and distilling saidsecond extract-mix phase separating said parainic hydrocarbon liquid asdistillate for recycle t-o said secondary extraction zone and remainingextract oil as a second extract product.

4. The process of claim 3 wherein said hydrocarbon oil feed comprises alubricating oil.

5. The process of claim 3 wherein said remaining extract-mix phase andsaid paraffinic hydrocarbon liquid are lcontacted at a temperaturewithin the range of about 90 to F. in said secondary extraction Zone.

'.7 8 6. The process of claim 3 wherein said remaining eX- ReferencesCited bythe Applicant tract-mix is contacted with said parainichydrocarbon at UNITED STATES PATENTS a paranic hydrocarbon dosage withinthe range of about 100 to 200 volume percent `of the remainingextract-mix. 1.211323 6/1938 Maey et a1- 5 2,216,932 10/1940 Atkins.References Cited by the Examiner 2,685,556 8/ 1954 HaChrIlllth. UNITEDSTATES PATENTS 2,727,848 12/1955 Georglan.

2,305,038 12/1942 Schumacher 208-312 DELBERT E. GANTZ, Primary Examiner.2,928,788 3/1960 Iezl 208-314 3,186,937 6/1965 Anderson et a1 208-314 10H LEVINE Asssm Examme

1. A METHOD OF TREATING A HYDROCARBON OIL WHEREIN SAID OIL IS CONTACTEDWITH A SELECTIVE SOLVENT COMPRISING FURFURAL IN A FIRST SOLVENTEXTRCTION ZONE UNDER CONDITIONS FORMING A FIRST RAFFINATE PHASE AND AFIRST EXTRACT-MIXPHASE, WHICH COMPRISES WITHDRAWING SAID FIRSTEXTRACT-MIX PHASE AT A TEMPERATURE WITHIN THE RANGE OF ABOUT 140 TO240*F., COOLING SAID FIRST EXTRACT-MIX PHASE TO A TEMPERATURE WITHIN THERANGE OF ABOUT 90 TO 120*F., SEPARATING A SECOND RAFFINATE COMPRISINGHYDROCARBON OIL EXTRACT AND DISSOLVED SOLVENT AND A SECOND EXTRACT-MIXPHASE COMPRISING SOLVENT AND REMAINING HYDROCARBON EXTRACT OIL,CONTACTING SAID SECOND EXTRACT-MIX PHASE WITH A LIQUID PARAFFINHYDROCARBON FRACTION BOILING WITHIN THE RANAGE OF ABOUT -44 TO 500*F.AND HAVING AN END POINT OF LEAST 100*F. BELOW THE INITIAL BOILING POINTOF SAID HYDROCRABON OIL IN A SECOND EXTRACTION ZONE FORMING A THIRDRAFFINATE PHASE COMPRISING SAID SELECTIVE SOLVENT AND A THIRDEXTRACT-MIX PHASE COMPRISING SAID REMAINING HYDROCRABON OIL AND SAID LOWBOILING HYDROCARBON, RECYCLING AT LEAST A PART OF SAID THIRD RAFFINATEPHASE TO SAID FIRST SOLVENT EXTRACTION ZONE AS AT LEAST A PORTION OFSAID SELECTIVE SOLVENT, SEPARATING HYDROCARBON EXTRACT OIL FROM SAIDSECONDARY RAFFINATE, AND SEPARATING REMAINING HYDROCARBON OIL EXTRACTFROM SAID THIRD EXTRACT-MIX.